Myopia control means

ABSTRACT

Sets, kits or stocks of anti-myopia contact or spectacle lenses, along with methods for their use, that do not require a clinician to measure peripheral refractive error in the eyes of myopic patients. Extensive surveys have shown that lenses having peripheral powers or defocus set in accordance with central corrective power will cover almost all normal myopes not worse than −6 D central refractive error. In one example, a kit or set of lenses ( 50 , FIG.  15 ) can have multiple parts or sub-sets ( 52, 54 ) each comprising a compartmented container ( 56   a,    56   b ) with lenses ( 58   a,    58   b ) arranged according to increments of central corrective power ( 59   a,    59   b ). The lenses ( 58   a ) of the first part ( 52 ) have four steps ( 60   a,    61   a,    62   a,    64   a ) of peripheral power or defocus to pro vide therapeutic effect and, while the lenses ( 58   b ) of the second part ( 54 ) also have four steps ( 60   b,    61   b,    62   b,    64   b ), the level of therapeutic effect is higher. Other examples of sets, kits and stocks, as well as examples of lenses themselves, are disclosed together with methods of use.

This application is a national stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/US2009/041103 filed Apr. 20, 2009,which claims benefits of Australian provisional application number2008901921 filed on Apr. 18, 2008 and of U.S. provisional applicationNo. 61/139,060 filed Dec. 19, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The current invention relates to means for inhibiting or amelioratingthe progression of myopia, particularly in young people, and includesboth methods and apparatus. The methods include procedures for theprescription, selection, fitting and supply of contact and spectaclelenses. The apparatus includes stocks, sets or kits of such lenses andto lenses or lens components per se.

In this specification contact and spectacle lenses capable of—orintended for—both correcting central refractive error and inhibiting theprogression (increasing severity) of myopia over time are termed‘anti-myopia’ lenses.

2. Background and Discussion of Prior Art

Myopia (short-sightedness) is a disorder of the eye in whichaccommodation of the natural lens can bring near objects but not distantobjects to focus on the central retina, distant objects being focused infront of (anterior to) the retina. That is, the focusing power of theeye is too strong ‘at distance’ for the accommodative power of the eye.The condition is corrected by the use of lenses with negative centralrefractive power which enable natural accommodation of the lens to focusboth near and distant objects on the fovea in the central portion of theretina. Hyperopia (long-sightedness) is a disorder where distant but notnear objects can be clearly focused, the condition being corrected bythe use of positive power lenses.

Progressive myopia, which is generally considered to be caused bygradually increasing eye length rather than lens power, can be a seriouscondition that leads to increasing visual impairment despite the use ofsuccessively stronger corrective lenses. Some countries in Asia arereporting that more than 80% of youths aged 17 years suffer from myopiaand that many are likely to have or develop the progressive condition.

It is generally agreed that normal eye development—calledemmetropization—is regulated by a feedback mechanism that controls eyelength to allow good central focus by accommodation at both distance andat near—called emmetropia—during animal growth. It is therefore assumedthat, in progressive myopia, this feedback mechanism goes awry andcauses the eye to continue to lengthen excessively even though goodcorrective lenses are used. Many conflicting theories have been advancedabout the nature of the feedback mechanism and, thus, many differenttreatments for progressive myopia have been proposed.

It has been proposed, for example, that the feedback mechanismcontrolling eye growth is somehow upset by deficiencies in theaccommodative effort of the eye due to excessive near work. Thedeficiency is considered to manifest as lag of accommodation (impreciseand insufficient accommodation) at near resulting in defocus, whichstimulates further undesirable axial elongation of the eye. Bifocallenses and PALs (progressive addition lenses) in spectacles were thusemployed to relieve the accommodative stress and defocus in the hopethat the stimulus for elongation would be removed. However, data fromclinical studies showed poor efficacy over the use standard refractivecorrection using negative power lenses.

U.S. Pat. No. 6,752,499 to Aller teaches prescribing commerciallyavailable concentric bifocal contact lenses for myopic eyes that alsoexhibit near point esophoria to control the progression of myopia. Bothdistance-center and near-center contact lenses were employed. Theselenses, in which both distance and near zones lie within the normalpupil diameter or ‘optic zone’ of the lens, have the disadvantage thatthey present two central images to the retina at all times so that imagequality is always degraded. In addition, the success of such treatmentmethods appears to be limited and variable.

In U.S. Pat. No. 6,045,578 to Collins et al. propose thatemmetropization is regulated by the degree and direction of sphericalaberration present at the fovea. It was proposed that young myopes havehigher levels of central negative spherical aberration which promotesinappropriate eye growth and that the use of therapeutic lenses toimpart positive central spherical aberration will inhibit excessiveaxial growth and thus the progression of myopia. We are not aware of thepublication of any significant comparative trial using lenses advocatedby Collins et al for controlling the progression of myopia. However, wenote that the additional spherical aberration further degrades centralimage quality for both near and distance vision and is, as before,inherently undesirable.

In WO 200604440A2, Phillips et al suggest that simple defocus at thefovea for both distance and near vision inhibits excessive eye growth.They therefore teach the use of a bifocal contact lens thatsimultaneously provides the central retina with (a) clear vision forboth distance and near and (b) myopic defocus for both distance andnear. Again, we are not aware of significant published trials reportingthe efficacy of this approach and note again that central vision isdegraded.

In contrast to the above, U.S. Pat. No. 7,025,460 to Smith et aldiscloses compelling results of animal trials which demonstrate that itis the nature of the peripheral image, not the central image, thatprovides the feedback stimulus for emmetropization. (These trials andexperiments have been published in prestigious peer-reviewed scientificjournals and have received widespread acceptance in the scientificcommunity.) Thus, Smith et al, teach that control of off-axis focus bymanipulation of the curvature of field to move the peripheral imageprogressively in front of the peripheral retina with increasingperipheral angle provides a method of abating, retarding or controllingthe progression of myopia. Lenses that manipulate the peripheral imagein this way are therefore called ‘anti-myopia’ lenses as they inhibitmyopia progression as well as providing correction of central refractiveerror. Smith et al noted that hypermetropia or hyperopia (impaired nearvision caused by insufficient eye length) could be addressed bymanipulation of the curvature of field to move the peripheral imageprogressively behind the peripheral retina.

International patent application WO/2007/146673 by Holden et aldisclosed two-zone anti-myopia lenses that are more easily designed andmanufactured than those which manipulate peripheral curvature of fieldin the manner taught by Smith et al. In such lenses, the central zonethat provides the refractive correction needed for good central visionapproximates the pupil diameter and is surrounded by a single-focustherapeutic peripheral zone having a refractive power tailored to moveat least portion of the peripheral image in front of the retina.

While we have confirmed the work of Smith et al and agree with Holden etal that a two-zone anti-myopia lens is easier to design and manufacture,the implementation of the Smith/Holden teachings in practice is stillnot straight forward as it requires instruments, training and facilitiesfor the measurement of peripheral refraction that are not widelyavailable, especially in the less affluent countries where progressivemyopia is a severe problem. The correct prescription of anti-myopialenses with a peripheral zone tailored to a patient's eye requires, forexample, (i) a peripheral refractometer that is capable of reliablydetermining peripheral focus, (ii) trained professionals who can usesuch refractometers with appropriate skill and who can accuratelyspecify the characteristics of corrective lens required for a particularpatient, as well as (iii) the presence of a lens manufacturing facilitythat is capable of making custom lenses with prescribed central andperipheral profiles to order. The associated costs may well put suchanti-myopia lenses beyond the reach of those most in need, despite beingsimpler to design and specify than the ‘progressive’ anti-myopia lensesof Smith et al.

At this point, three matters of terminology need to be clarified: howthe severity of myopia is indicated, the difference between conventionalbifocal lenses and anti-myopia lenses, and, the use of absolute andrelative terms to indicate the peripheral power of a lens.

First, it is conventional to refer to a patient as, say, a ‘minus 3 Dmyope’ meaning that the patient needs or wears −3 Diopter (“D”)corrective lenses. This can be confusing because the patient has a +3 Drefractive error and could—with some logic—be called ‘a +3 D myope’.Since the conventional terminology is entrenched, it will be used hereinbut care will be taken herein to indicate whether the refractive errorof the eye or the power of the corrective lens is intended.

Second, a conventional bifocal lens has two central optic zones ofdifferent refractive power, one enabling good central distance visionand the other enabling good central near vision. In bifocal spectaclelenses, the near zone is formed in the lower portion of the lens and thedistance zone is formed in the central and/or upper portions of thelens. This allows the desired zone and image to be automaticallyselected by normal eye movement so a single image is presented to theeye. Because conventional bifocal contact lenses are located on thecornea and move with the eye, both the distance and near zones arelocated in the central portion of the lens that approximates normalpupil diameter. Thus, both the corrected distance and near images arealways presented to the fovea simultaneously and it is left to the brainto direct attention to one or the other, but each image is necessarilydegraded by the other. Anti-myopia lenses are not inherently—or evenpreferably—bifocal in that they are not concerned to provide good nearand distance central vision using different central optical zones.Instead, anti-myopia lenses normally have a central refractive zone tocorrect central myopic refractive error and provide good central visionand a peripheral ‘therapeutic’ refractive zone outside the central zoneto inhibit continued eye growth. However, anti-myopia lenses can bebifocal, in which case they would have two central zones like aconventional bifocal lens in addition to the therapeutic peripheralzone.

Third, the difference between the refractive power of the central andperipheral zones of an anti-myopia lens is often referred to as‘peripheral defocus’ because it is conventional to specify lenses interms of a base corrective refractive power applied to the whole opticzone and to regard a different power in the periphery to be amodification of the base power. Thus, when the peripheral refractivepower is less negative than the central power, the corrective lens issaid to have peripheral ‘myopic defocus’ and, when the peripheralrefractive power is more negative than the central power, the lens issaid to have ‘hyperopic defocus’ in the periphery. This is confusing ifthe change in peripheral power improves focus in the periphery. On theother hand, as the peripheral defocus of many anti-myopia lenses isincreased to ensure that the peripheral image is in front of the retina,these lenses may cause focal error or blur in the peripheral retina. Inthis specification, ‘peripheral defocus’ will be used conventionally forthe relative difference between peripheral and central refractive powerof an anti-myopia lens and ‘peripheral power’ will indicate the absoluterefractive power in the periphery of the optic zone of a lens. It willbe appreciated, however, that peripheral defocus and peripheral powerare essentially equivalent since one can readily be derived from theother if the central power of the lens is known. It should also be notedthat the peripheral defocus may be different for different radialdistances on a lens if the peripheral power and/or central power of thelens is not constant with radius. Finally, the peripheral mis-focusperceived by a patient fitted with an anti-myopia contact or spectaclelens will be called ‘blur’ or ‘peripheral blur’.

BRIEF SUMMARY OF THE INVENTION

While we appreciate the scientific contribution of Smith et al, aspublished in both the scientific and patent literature, and while werecognize the practical benefit of the two-zone anti-myopia lensesproposed by Holden et al, we are nevertheless concerned about the costof providing Smith/Holden anti-myopia lenses and therapies to myopes,particularly to young myopes in developing countries where progressivemyopia is common and debilitating.

Since our research indicated that the optimal area of the peripheralimage to manipulate for a two-zone anti-myopia lens is that affected byan incident peripheral ray at an angle of about 30 degrees, we undertookextensive surveys of the eyes of young myopes in Australia and China inwhich central and peripheral refractive errors were measured at thisangle both with and without their conventional corrective lenses inplace. Peripheral error was measured at approximately 30 degrees to thevisual axis for the temporal, nasal and superior quadrants of theretina. From other studies, we also considered that—as far as theproblem of progressive myopia is concerned—the population of youngmyopes surveyed is generally representative of −0.25 D to −6 D myopesworldwide. This cohort or group can be termed ‘normal myopes’ todistinguish them from extreme or pathological myopes that aresignificantly worse than −6 D. In short, we believe that our strategiesfor inhibiting progressive myopia, as disclosed herein, can be generallyapplied to normal myopes. The survey data is summarized in FIGS. 3-11but more detailed and technical publications will occur in thescientific literature.

In summary, our survey data revealed that:

-   (i) Surprisingly, and in apparent conflict with the teachings of    Smith et al, almost all unaided eyes with significant myopia    (greater than +1.75 D central refractive error) were not hyperopic    in the periphery. Only those with central refractive errors less    than +1.75 D were slightly (less than −1.0 D) hyperopic in the    periphery, and this tended to be in the temporal quadrant of the    eye.-   (ii) The degree of peripheral refractive error at 30 degrees    (incident) in the unaided eye is generally positively related to the    degree of central refractive error, being more closely proportional    in the nasal meridian. For unaided eyes with central refractive    errors increasing from about +1.75 D to about +3.75 D this    peripheral refractive error increased roughly proportionately from    zero to about +2 D and, for central errors increasing from about    +4.0 D to about +6.0 D, the peripheral error increased from about    +2.0 D to a little over about +4.0 D, again in substantial    proportion.-   (iii) Thus, instead of the worst unaided myopes being the most    hyperopic in the periphery they were the most myopic; that is, they    should have had the greatest inhibition of eye growth according to    Smith et al.

The apparent conflict between our survey findings and the teachings ofSmith et al is readily resolved when overall refractive errors aremeasured on ‘aided eyes’; that is, with the subject's habitual contactor spectacle lenses in place. It is then found that practically allaided myopic eyes are hyperopic in the periphery and that the greaterthe central refractive correction the greater the peripheral hyperopia.In other words, by making the power of the conventional lenssufficiently negative to bring the central focus onto the retina, theperipheral focus of the aided eye is moved back behind the retina makingthe periphery hyperopic and generating the stimulus for further eyegrowth. Ironically, for −4 D to −6 D myopes (ie, at the higher end ofnormal), any therapeutic benefit of their substantial (unaided)peripheral myopia is swamped by the peripheral hyperopia imposed bycorrective lenses of conventional design. In short, the results of oursurvey strongly support the basic hypothesis of Smith et al.

Our investigations have shown that the great majority of myopes willaccept contact lenses that have 3.0 D myopic peripheral defocus at 30degrees (incident) and that many will tolerate or get used to aperipheral defocus as high as 3.5 D. Combining this information with thebroad survey findings outlined above showed that there is a very highstatistical probability (around 95%) that contact-lens-wearing −6 Dmyopes or better can be fitted from a stock of pre-manufacturedanti-myopia contact lenses with a lens that both corrects central errorand has a pre-set myopic peripheral defocus sufficient to mitigatemyopia progression without intolerable peripheral blur.

While the situation with spectacle-wearing myopes is nominally much thesame as for contact lens wearers, their tolerance for peripheral blurmay be somewhat reduced because of ‘swim’; that is, peripheral blur thatchanges with eye movement. However, the amount of swim can be generallyreduced by adjustment of the base curve of the spectacle lenses.

Producing, using and supplying pre-manufactured sets, kits or stocks ofanti-myopia lenses with pre-determined corrective and peripheral powerstherefore comprise one aspect of this invention. Another aspect ispre-assembled or pre-manufactured sets, kits or stocks in which thelenses are organized or arrayed according to corrective power and/oraccording to steps or levels of peripheral defocus so that use andunderstanding of anti-myopia lenses by clinicians and patients isfacilitated. For example, understanding can be facilitated by using onlya few steps of peripheral power (so that multiple lenses within a bandof central powers share the same peripheral power). In addition oralternatively, a kit with multiple anti-myopia lenses having the samecentral corrective power but differing levels of peripheral power enablea clinician to select a level of peripheral power, defocus ortherapeutic effect based on assessed patient propensity for progressivemyopia. Another aspect of the invention therefore relates to methods ofprescription and/or trial fitting using the anti-myopia lenses of thepresent invention.

For contact lenses, it is preferable that the central corrective powerof the anti-myopia lenses of the set, kit or stock increases inincrements of about −0.25 D, giving about 20 increments over −5 D orabout 24 increments over −6 D, but other increments may be used. Alarger number lenses with smaller increments is possible but generallynot cost-effective while fewer lenses with large increments—for example,−0.33 D or even −0.50 D—may save cost but be less than optimal for thepatient. It will be appreciated that the set or kit of contact lensesmay include multiple copies or batches of each lens to form a stock ofidentical lenses to allow multiple identical prescriptions or fittingswithout the need to restock the set. Normally, the contact lenses willbe hygienically packed in sachets identifying the central correctivepower, peripheral power or defocus and the treatment level (amount ofperipheral defocus). Also, it will be appreciated that not every set,kit or stock of contact lenses formed in accordance with this inventionneeds to have a full complement of lenses from, say, −0.25 D to −6.0 D,as smaller kits may be more appropriate for specialist clinicians whoprefer to treat only certain classes of patients.

The stocks, sets or kits for spectacle lenses can be of quite adifferent character to those indicated above for contact lenses becausethey may only comprise a few add-on (eg, clip-on or stick-on) lensesapplied to the spectacles used by the patient. Such add-on lenses canhave plano center zones and offer the choice of just a few levels ofperipheral myopic defocus or power to be selected according to desiredtherapeutic effect and/or patient tolerance to swim. Here, ‘plano’ meanscontributing negligible refractive power to the combined lens. Thusadd-on lenses with plano central zones maybe transparent lenticulardiscs in which the central material has negligible optical power, orthey may be ring-like in that there is a central hole rather than anycentral material. The former are preferred because the physical edge ofa hole is avoided and the transition between the plano center and theselected peripheral power can be made gradual. Also, if the add-on lensis not rigid (as in a clip-on lens) but is floppy (as in a peel-off andstick-on sheet-like lens), thin stick-on discs can be more easilyhandled than thin rings. From another aspect, the invention alsocomprises add-on spectacle lenses of the type indicated for convertingstandard spectacle lenses into anti-myopia lenses.

Alternatively, sets, kits or stocks of pre-manufactured finishedanti-myopia spectacle lenses with increments of central power and withsteps and/or levels of peripheral power (as described above for contactlenses) may be provided or used with the advantage of precision, despitethe additional cost involved. Further, bearing in mind the problem ofswim in some spectacle lenses, the number or range of pre-manufacturedspectacle lenses may be less than for contact lenses. The precisematching of the peripheral and central powers enabled by complete kitsof finished trial spectacle lenses can be of particular value for largeclinics that have turnkey facilities for finishing base lenses in-house.It will also be appreciated that both contact and spectacle lensesenvisaged herein may be rotationally symmetric or asymmetric; that is,some may have substantially the same peripheral defocus in all quadrantswhile others may have different levels of defocus in differentquadrants.

The need for a clinician to measure peripheral refraction of an eye,calculate the adjustment required to secure the desired therapeuticeffect, specify a custom lens and have it supplied is thus avoided bythe availability of such sets of pre-manufactured anti-myopia lenses.While it is preferable for the clinician to have a set of anti-myopialenses for trial fitting and/or supply to patients, it may suffice forthe clinician to simply determine the central refractive error and thefit or style of the lens and to then order an anti-myopia lens with theappropriate central correction and shape from a stock or kit of lensesheld by a manufacturer or wholesaler.

From another aspect, the invention comprises a set, kit or stock ofpre-manufactured lenses for providing an anti-myopia lens for an eye ofa myopic patient, where each lens has a central optical axis and acentral optical zone with a corrective refractive power of less thanabout −6.0 D and each lens has a peripheral optical zone lying outsidethe central zone that includes incident angles of around 30 degrees andthat has myopic defocus of not more than about 3.5 D. The lenses may berotationally symmetric having the same peripheral defocus in allquadrants or they may be asymmetric in that the peripheral defocus isconcentrated in selected quadrants, the nasal and temporal quadrants ofthe lenses being preferred. The lenses of the set are arranged in anorderly manner so that a clinician, by selecting a lens for centralcorrective power, is able to provide a lens which inhibits myopiaprogression without needing to measure peripheral refractive error inthe eye and prescribe a lens with customized peripheral power.

From another aspect, the invention comprises an anti-myopia spectaclelens formed from a base lens with a central corrective optical zone ofat least normal pupil diameter, and a therapeutic lens with a planocenter attached to the base lens. The therapeutic lens has an annularperipheral zone surrounding the plano center of sufficient size toinclude incident angles of around 30 degrees and has refractive powerthat is more positive than that of the central corrective zone of thebase lens.

From another aspect, the invention comprises a method of supplying orselecting an anti-myopia lens for a myopic eye which includes the stepsof: measuring the central refractive error of the myopic eye, assessingthe propensity of the patient for progressive myopia by having regard topatient history, selecting from a set, kit or stock of pre-manufacturedlenses a first lens having (i) a central corrective refractive powerthat best matches the measured central refractive error and (ii) a levelof peripheral myopic defocus that best matches the assessed propensityfor progressive myopia, trying the first lens on the eye to determinewhether the peripheral blur is acceptable and, if so, supplying orprescribing the first lens. If the level of myopic defocus isunacceptable, a second trial lens is selected from the set, kit or stockof with the same the same central corrective power but a reduced levelof peripheral myopic defocus.

From another aspect, the method may employ a set, kit or stock of lenseshaving multiple lenses with the same central corrective refractive powerbut with different levels of myopic peripheral defocus, the method thencomprising the steps of: measuring the central refractive error of themyopic eye, taking the patient's history to assess the patient'spropensity for progressive myopia, and supplying, prescribing orselecting a lens having (i) a central refractive power to correct themeasured refractive error and (ii) the level of myopic peripheraldefocus corresponding to assessed propensity for progressive myopia.

From another aspect, the invention can involve a method of providing ananti-myopia spectacle lens having the steps of: measuring the centralrefractive error of the eye, judging the propensity of the patient forprogressive myopia from the patient history, prescribing and fitting aconventional spectacle lens for the eye to correct the error, selectingan auxiliary lens with a plano central zone surrounded by a peripheralzone with a positive peripheral power appropriate to the judgedpropensity of the patient for progressive myopia, and coaxiallyattaching the auxiliary lens to the conventional lens so that thecombination of the conventional and auxiliary lens generates aperipheral defocus for inhibiting the progression of myopia in the eye.

From another aspect the invention provides an ophthalmic device, forexample an ophthalmic lens, such as a contact lens, for reducing theprogression of myopia of an eye, the ophthalmic device comprising apredetermined central sphere power which is defined by an amount ofmyopia of an eye, and includes a predetermined peripheral power profilewhich effects a relative peripheral refraction of a corrected eye andwhich peripheral power profile defines a peripheral defocus. Theperipheral defocus is a differential between the central sphere powerand the peripheral sphere power along the peripheral power profile,wherein the peripheral defocus is a function of the central spherepower.

From another aspect the invention provides a method for reducing theprogression of myopia of an eye, the method comprising placing anophthalmic device, for example a contact lens, on an eye wherein thedevice comprises a predetermined central sphere power which is definedby an amount of myopia of an eye, the device further including apredetermined peripheral power profile which effects a myopic defocus,and including a peripheral defocus of the peripheral power profile,wherein the peripheral defocus is a differential between the centralsphere power and the peripheral power along the peripheral powerprofile, wherein the peripheral defocus is a function of the centralsphere power.

From another aspect the invention provides a ophthalmic device, forexample a contact lens, for reducing the progression of myopia of aneye, the device including a predetermined central sphero-cylindricalpower which is defined by an amount of myopia of an eye, a predeterminedperipheral power profile which effects a relative peripheral refractionof a corrected eye and a peripheral defocus of the peripheral powerprofile, wherein the peripheral defocus is a differential between thecentral sphero-cylindrical power and the peripheral sphere power alongthe peripheral power profile, and wherein the peripheral defocus is afunction of the central sphero-cylindrical power.

In embodiments of these aspects, the peripheral defocus may be definedby the average amount of relative peripheral refraction in a populationby sphere power. The peripheral defocus may be approximately first orderlinear as a constant function of the central sphere power, or may benon-linear as a function of the central sphere power, or may increasenon-linearly or decrease non-linearly as a function of the centralsphere power. The peripheral defocus up to 30 degrees from the centralaxis may be between about 0.25 D and 4.00 D, and/or the peripheraldefocus up to 40 degrees from the central axis may be between about 0.5D and about 6.00 D. Also, the ophthalmic device may be part of a seriesof ophthalmic devices comprising an ophthalmic device having an averageperipheral defocus, an ophthalmic device having an above averageperipheral defocus and an ophthalmic device having a below averageperipheral defocus, wherein the average peripheral defocus is determinedby a mean from a defined population.

These and other features and advantages of the invention will beunderstood with reference to the drawing figures and detaileddescription herein, and will be realized by means of the variouselements and combinations particularly pointed out in the appendedclaims. It is to be understood that both the foregoing generaldescription and the following brief description of the drawings anddetailed description of the invention are exemplary and explanatory ofpreferred embodiments of the invention, and are not restrictive of theinvention, as claimed.

DESCRIPTION Brief Description of the Drawings

FIG. 1 is a diagrammatic sectional plan of a emmetropic human eyeshowing various incident light rays to clarify the meaning of terms usedin this specification.

FIG. 2 is a similar diagram to that of FIG. 1 but illustrates—in anexaggerated manner—refractive errors of a typical myopic eye.

FIG. 3 is a similar diagram to that of FIG. 2 but illustrates the use ofa normal lens for correcting central refractive error.

FIG. 4 is a similar diagram to that of FIG. 2 but illustrates the use ofan anti-myopia contact lens.

FIG. 5 is a similar diagram to that of FIG. 2 but illustrates the use ofan add-on lens and a normal spectacle lens as a combined anti-myopialens.

FIG. 6 is a scatter plot of spherical equivalent corrective power neededfor peripheral rays in the temporal retina against central sphericalequivalent corrective power of unaided eyes obtained from a large surveyof youthful Australian and Chinese myopes.

FIG. 7 is a scatter plot of spherical equivalent corrective power forthe peripheral nasal retina quadrant against central sphericalequivalent corrective power obtained from the survey of FIG. 6.

FIG. 8 is a scatter plot of spherical equivalent corrective power forthe peripheral superior retina quadrant against central sphericalequivalent corrective power obtained from the survey of FIGS. 6 and 7.

FIG. 9 is a scatter plot of central corrective power vs. mean horizontalperipheral corrective power and central corrective power vs. temporalperipheral corrective power, with best-fit linear regression lines shownfor each, obtained from the survey of FIGS. 6 and 7.

FIG. 10 is a scatter plot of central corrective power vs. meanhorizontal corrective peripheral power and central corrective power vs.nasal quadrant corrective power, with best-fit linear regression linesshown for each, obtained from the survey of FIGS. 6 and 7.

FIG. 11 is a scatter plot of mean horizontal corrective power againstspherical corrective central power, obtained from the survey of FIG. 6.

FIG. 12 is a tabulation based upon the survey results of FIGS. 6-11relating measured central and median peripheral refractive errors todifferent sets of anti-myopia lens characteristics.

FIG. 13 is a tabulation also based upon the survey results of FIGS. 6-11relating measured, central, nasal and temporal refractive errors toadditional different sets of anti-myopia lens characteristics.

FIG. 14 is a graph showing peripheral defocus power curves of fourexemplary contact lens designs that are consistent with the “Mild”prescription option of the table of FIG. 12.

FIG. 15 is a diagrammatic representation of a two part trial kit oflenses suitable for use by a practitioner for both correcting myopia andinhibiting the progression of myopia in patients.

FIG. 16 is a diagrammatic representation of a trial and dispensing kit,set or stock of contact lenses.

FIG. 17 is a diagrammatic representation of a small kit of add-onspectacle lenses.

FIG. 18 represents the central and peripheral auto refraction of an eyewhich is emmetropic with power (D) in the y axis and offset (in degrees)from the central axis in the x axis.

FIG. 19 shows the peripheral auto refraction of an eye which is highly(with a subjective central refraction of about −6.00 D) myopic withpower (D) in the y axis and offset (in degrees) from the central axis inthe x axis.

FIG. 20 shows the peripheral auto refraction of an eye myopic eye with asubjective central refraction of about −1.50 D and the peripheral autorefraction through a soft contact lens with a high peripheral defocuswith power (D) in the y axis and offset (in degrees) from the centralaxis in the x axis.

FIG. 21 shows the peripheral auto refraction of same highly myopic eyeas in FIG. 19 and the peripheral auto refraction through a soft contactlens with a high peripheral defocus with power (D) in the y axis andoffset (in degrees) from the central axis in the x axis.

FIG. 22 shows the results of a study of Schmid in which the sphere powerin minus cylinder notation was measured centrally and at 20 degrees inthe nasal, temporal, inferior and superior retina with central spherepower (D) in the X axis and peripheral differential power (D) in the Yaxis.

FIG. 23 shows more details on the study of Schmid and separates thenasal, temporal, inferior and superior data with central sphere power(D) in the X axis and peripheral differential power (D) in the Y axis.

FIG. 24 is a representation of the effect of peripheral refraction interms of sphere refraction and sphere equivalent on rated side visionquality.

FIG. 25 is a graph plotting central sphere equivalent refraction againstthe refractive difference between central and 30 degree nasally offsetautorefractions, for both sphere meridian and sphere equivalents.

FIG. 26 is a graph plotting central sphere equivalent refraction againstthe refractive difference (sphere equivalent) between central and 30degree nasally offset autorefractions, for two test populations.

FIG. 27 is a representation of an example lens provision scheme having“Low”, “Average” and “High” target correction series.

FIG. 1 is a greatly simplified diagrammatic sectional plan of a normalleft human eye 10 having a cornea 12, iris 14, lens 16, retina 18 andvisual axis 20, the nasal plane between the eyes (or mid-visual axis)being indicated at 21. Retina 18 is divided into (i) a central portion22 (solid black) that is used for central vision and includes the fovea,the most sensitive portion of the retina, and (ii) an annular peripheralportion 24 (hatched) which is much larger in area than central portion22 but is less sensitive. In a normal or emmetropic eye with astraight-ahead gaze (on axis 20) directed at distance, an axial centralbeam 26 from a distant object will be brought to focus at f on the foveain the middle of central region 22 of retina 18 providing good visualacuity. At the same time, a peripheral or off-axis beam 28 from adistant object will be brought to focus at point p on peripheral retina24, it being assumed that the central ray 28 a of peripheral beam 28intersects visual axis 20 at the axial center n of pupil 14 (sometimesreferred to as the nodal point of eye 10). When the gaze is directed ata near on-axis object, the lens 16 changes shape and optical power in aprocess called ‘accommodation’ to (ideally) also bring beam 26 from thenear object to focus at point f. Similarly, beam 28 from a near off-axisobject ideally will be brought to focus at point p on peripheral retina24. In fact, an emmetropic eye will normally exhibit astigmatism forperipheral off-axis objects so that there will be two slightly differentfoci near p on the peripheral retina for both near and distance images.

It will be noted by inspection of FIG. 1 that peripheral beam 28 enterseye 10 from the temporal side or quadrant of the eye (and head) and isfocused on the nasal side or quadrant of peripheral retina 24.Conversely, though not shown, peripheral rays entering eye 10 from thenasal quadrant will impinge on the temporal quadrant of peripheralretina 24. Of course, peripheral rays can enter the eye from thesuperior quadrant (above) or the inferior quadrant (below).

The work of Smith et al has shown that out-of-focus images on theperipheral retina 24 provide an important stimulus for the regulation ofeye growth. Accordingly, the measurement of the refractive power of theeye at off-axis angles is now considered to be of critical importancefor correctly prescribing lenses for myopes suffering from progressivemyopia. In this specification, the angle α at which central ray 28 a ofperipheral beam 28 intersects axis 20 at point n is the peripheral angle(or off-axis angle) of that ray or beam. Because of refraction at thecornea 12 and lens 16, the angle β which the emergent central peripheralray 28 b makes with optic axis 20 within eye 10 is less than α and isdifficult to determine in vivo with normally available instruments. Itis noted that the axial distance between the anterior surface of cornea12 and the plane of iris 14—often referred to as the anterior chamberdepth, or ACD—is generally taken to be 3.5 mm. This distance isidentified as ACD in FIGS. 1-3 and is used in measuring the peripheralpowers of anti-myopia lenses.

Our research suggests that an incident angle α of 30 degrees in anymeridian will place point p far enough into the peripheral retina toprovide the desired stimulus for eye growth but is not so oblique as tobe excessively difficult to use. Effectively, angle α can be regarded asa solid angle. Accordingly, in our extensive surveys of myopic youth inAustralia and China we used an incident peripheral angle α of 30 degreeswhen measuring the peripheral refraction of aided and unaided eyes. Thefindings of these surveys have therefore been used to design and testcorrective symmetrical and asymmetrical anti-myopia lenses for myopicpatients generally.

FIG. 2 is essentially the same diagram as that of FIG. 1 but shows (verymuch exaggerated) a myopic eye 10 a that is also prone to progressivemyopia. (The same reference numerals are used for the same parts as ineye 10 of FIG. 1.) The axial length of eye 10 a is too long foraccommodation to focus on-axis beam 26 from a distant object ontocentral retina 22. Instead, it is focused at point f′ in front ofcentral retina 22 and distant images will therefore be out-of-focus. Forconvenience, this problem is commonly regarded as ‘refractive error’because can be corrected by fitting a negative power lens (see FIG. 3).However, myopes can typically focus near on-axis objects on central theretina 22 achieve good near vision. Eye 10 a illustrates another‘refractive error’ common in myopic eyes—peripheral hyperopic defocus—inwhich off-axis beam 28 is focused behind peripheral retina 24, at p′.Smith et al have shown that hyperopic defocus increases the stimulus forexcessive eye growth and contributes to progressive myopia.

FIG. 3 shows myopic eye 10 a fitted with a conventional corrective lens.Though a spectacle lens 30 is illustrated, the same considerations applyto conventional contact lenses. Lens 30 has negative power that nicelycorrects central vision to let accommodation of natural lens 16 bringon-axis beam 26 from a distant object to focus on the fovea at f.However, lens 30 shifts the focus of off-axis beam 28 to a point p″further behind peripheral retina 24, generating an even greater stimulusfor continued eye growth and progressive myopia. FIG. 4 illustrates theeffect of an anti-myopia corrective lens on myopic eye 10 a, in thiscase a contact lens 32. Lens 32 has a central optic zone 32 a of aboutpupil size (normally 4-5 mm diameter for youths under standard roomlighting) that corrects central vision to let accommodation of naturallens 16 bring distance central focus onto central retina 22 at point f.Lens 32 has an annular peripheral therapeutic optic zone 32 bsurrounding central zone 32 a with sufficient myopic defocus to bringperipheral beam 28 to focus at point p″ in front of peripheral retina24, thereby generating a stimulus to inhibit eye growth and progressionof myopia in eye 10 a. However, the out-of-focus peripheral image cancause peripheral blur. Contact lens 32 has a non-optic zone 32 csurrounding peripheral zone 32 b to enhance fitting and comfort.

FIG. 5 shows the conversion of conventional spectacle lens 30 in FIG. 3to an anti-myopia lens with the same effect as contact lens 32 by theaddition of an add-on lens 34. Lens 34 has a plano central optic zone 36that does not affect the central refractive power of base spectacle lens30 so that central beam 26 can still be brought to focus at point f onthe fovea of central retina 22. However, add-on lens 34 has an annular aperipheral refractive zone 38 with positive power that, despite thenegative power of lens 30, generates sufficient peripheral myopicdefocus to bring off-axis beam 28 to focus at point p′″ in front ofperipheral retina 24 (as in the case of contact lens 32, FIG. 4). Add-onlens 34 can be attached by mechanical clips 40 to base lens 30 (or to aspectacle frame, not shown), or it may be attached by a suitableadhesive.

Those skilled in the art will appreciate that there are known ways inwhich the refractive powers of the different zones of multi-zoneartificial lenses can be measured in different quadrants, and in whichthe peripheral and central focal points of aided and un-aided eyes canbe determined. International patent applications WO/2008116270 andPCT/AU2008/000434 by Erhmann et al respectively disclose techniques formapping the refractive power of lenses and the eye at large peripheralangles.

The extensive surveys of youth in Australia and China that we haveconducted in which we measured peripheral refractive error at 30 degrees(incident) in the nasal, temporal and superior quadrants confirmed thatmost (but not all myopes) have hyperopic defocus, but the amount was notas great as anticipated and did not increase as dramatically as expectedfor high myopes. Data from the myopic eyes included in these surveys hasbeen condensed into the graphs or scatter charts of FIGS. 6-11 in whichthe refractive power of an eye is measured in terms of the sphericalequivalent, and in which all peripheral measurements were made at 30degrees (incident) in various quadrants. These graphs can be summarizedas follows.

FIG. 6 plots peripheral corrective refractive power (as sphericalequivalent) of the surveyed eyes at 30 degrees in the temporal quadrantagainst central (on-axis) corrective refractive power (also as sphericalequivalent), indicating a generally linear relationship. It will be seenthat there is a 3 D spread in peripheral focus for mild myopes (betterthan −2 D), with most eyes exhibiting hyperopic (relative) defocus inthe periphery. Those exhibiting hyperopic defocus would be considered tobe a much greater risk for progressive myopia than those with myopicdefocus. Similar results are evident for measurements of correctiveperipheral powers in the nasal and superior quadrants—FIGS. 7 and 8respectively—but with a significantly greater spread of correctiveperipheral powers, especially in the superior quadrant.

FIGS. 9 and 10 present the corrective temporal and nasal power data ofFIGS. 6 and 7. FIG. 9 plots corrective central vs. corrective meanhorizontal power and corrective central vs. corrective temporal power,with best-fit linear regression lines shown for each. FIG. 10 plotscorrective central vs. corrective mean horizontal power and correctivecentral vs. corrective nasal power, with best-fit linear regressionlines shown for each. Finally, if the mean corrective horizontal poweris plotted against the corrective spherical central power, as in FIG.11, it will be seen that almost all of the survey population fall withina 3 D spread.

Clearly, this data supports the basis of the present invention; namely,that the peripheral power of anti-myopia lenses for normal myopes can bepre-set according to central power without peripheral defocus exceeding3 D, thus avoiding the need to measure peripheral refractive error inthe eye and prescribe customized lenses to both correct centralrefractive error and to appropriately control peripheral refraction fortherapeutic purposes. Furthermore, the data can be reduced to usefullook-up tables or rules of thumb that correlate the median spheredifference between central and peripheral power for rotationallysymmetrical lenses (as in FIG. 12) or for rotationally asymmetric lenseshaving different temporal and nasal powers (as in FIG. 13).

Referring more specifically to FIG. 12, the left hand column [CentralRefractive Error (D)] lists measured central refractive error inincreasing increments of +0.25 D up to +6.00 D for the unaided eyes ofthe surveyed population. The second column from the left [MedianPeripheral Refractive Error (D)] reports the measured median peripheralrefractive error at 30 degrees (incident). Thus, −0.25 D myopes (thosewith a central refractive error of +0.25 D) were found, on average, tobe −0.71 D hyperopic periphery and −5 D myopes of the population (thosewith a central refractive error of +5.00 D) were found, on average, tobe +2.83 D myopic in the periphery. The third column [Median Script(Survey) Cent/Periph.] of the table of FIG. 12 indicates the absolutecentral and the peripheral defocus (respectively) of a customizedprescription lens appropriate, on average, for the part of the surveyedpopulation having the corresponding central and peripheral refractiveerrors indicated in the first two columns of FIG. 12. Thus a −0.25 Dmyope (with a +0.25 measured central error) requires a lens with acorrective central power of −0.25 D and a peripheral defocus of +0.96 Dto (i) provide both good central vision and (ii) bring the peripheralfocus (at 30 degrees incident) in front of the retina so as tosubstantially eliminate the stimulus for excessive eye growth.Similarly, a −5.0 D myope requires a corrective central power of −5.00 Dand a peripheral defocus of +2.17 D for good vision and to substantiallyeliminate the stimulus for eye growth. Thus, the third column of FIG. 12defines a pre-manufactured set, kit or stock of anti-myopia lenses withminimal pre-set peripheral powers. Conveniently, these lenses can berotationally symmetric.

The two-part fourth column [Add Stepped Peripheral Power/Defocus toLens] of the table of FIG. 12 indicates mild and high treatment options(levels of peripheral defocus) that may be used to provide correspondingmedium and high levels of corrective stimulus for reducing eye growth.The ‘mild’ option adds +1.00 D, +1.50 D, +2.00 D and +2.50 D in fourdiscrete steps of peripheral defocus, which increase the level ofdefocus over the minimal-treatment lenses of the third column of FIG.12, while the ‘high’ level adds +1.50 D, +2.00 D, +2.50 D and +3.00 D infour steps of peripheral defocus. The use of steps in peripheral defocus(ie, where multiple lenses with the same central power have differenceperipheral powers) is intended to simplify understanding andprescription by patients, clinicians and manufacturers. The lenses ofthe two-part fourth column of FIG. 12 are also conveniently rotationallyasymmetric.

Referring more particularly to FIG. 13, the table of this Figureprovides information useful in the case of manufacturing rotationallyasymmetric lenses having different temporal and nasal powers. The lefthand column [Central Refractive Error (D)] again lists increments ofmeasured central refractive error in increasing increments of +0.25 D upto +6.00 D (for −0.25 D to −6.0 D myopes). The second column from theleft [Median Temporal Refractive Error (D)] reports the median measuredtemporal refractive error for those of the surveyed population havingthe corresponding increment of measured central refractive error listedin the left hand column of FIG. 13. The third column from the left[Median Nasal Refractive Peripheral Error (D)] reports the measuredmedian nasal refractive error for subjects having the correspondingcentral refractive error listed in the left-most column. It is notedthat the surveyed population were somewhat more hyperopic in thetemporal retina than in the nasal retina, suggesting that it might beadvantageous to use the temporal retina measurements.

The fourth column [Median Script (Survey) Cent/Temporal] of the table ofFIG. 13 can be regarded as defining a set of asymmetric anti-myopialenses with minimal therapeutic power applied in the temporal quadrantof the retina, the second powers in the column being peripheral defocusin that quadrant. It is to be noted that the lenses will have theperipheral defocus applied to their nasal quadrants to affect thetemporal retinal quadrant. Similarly, the fifth column [Median Script(Survey) Cent/Nasal] of FIG. 13 can be regarded as defining a set ofasymmetric anti-myopia lenses with minimal therapeutic power applied tothe nasal quadrant of the retina. Again, it is to be noted that thelenses of the set of the fifth column will have the peripheral defocusapplied to their temporal quadrants to affect the nasal retinalquadrant.

The split sixth column [Added Stepped Peripheral Power] of the table ofFIG. 13 indicates steps of peripheral defocus that can be used to modifyperipheral defocus of the sets of lenses of the fourth and fifthcolumns. As shown, the column entitled “Temporal Chosen Power/Defocus”applies the peripheral defocus to the lenses of the ‘temporal set’ infour discrete steps, +1.5 D, +2.0 D, +2.5 D and +3.0 D to the temporalcorrective power, while the “Nasal Chosen Power/Defocus” (right handcolumn) applies the peripheral defocus to the lenses of the ‘nasal set’in three distinct steps, +1.0 D, +1.5 D and +2.0 D. Again, It should benoted again that, when considering lens design, it is the nasal andtemporal quadrants (respectively) of the lenses to which the peripheraldefocus is applied to effect the desired changes in the peripheraltemporal and nasal quadrants of the retina. The lenses of the two-partfourth column of FIG. 13 [Add Stepped Peripheral Power] are, of course,rotationally asymmetric.

FIG. 14 illustrates the relative power curves for each of the four stepsof peripheral defocus of the contact lenses designed according to the‘Mild’ option of FIG. 12 (fourth column). The maximum peripheral defocusof the lenses of this subset or option is set at 2.5 D. The referencenumerals (60 a, 61 a, 62 a and 64 a) applied to the power curves areused in describing the two part trial kit of FIG. 15 below.

FIG. 15 is a diagrammatic representation of a two part trial orprescribing lens kit or set suitable for practitioners, which can besubstituted for conventional kits at little extra cost and can comprisea kit or set of finished trial spectacle lenses or a kit or set of trialor dispensing contact lenses. This Figure can be viewed as adiagrammatic plan view of a single drawer or tray 50 in which lenses arearranged in two arrays or parts 52 and 54 on a single level, or it canbe viewed as a diagrammatic sectional elevation of a cabinet 50 that hastwo drawers or parts 52 and 54, one above the other. The lenses of part52 conform to those set out in the ‘Mild’ peripheral power column(second from right) while the lenses of part 54 conform to those set outin the ‘High’ peripheral power (far right) of the tabulation of FIG. 12.Thus, kit or set 50 has double the minimum number of lenses need for akit covering ‘normal myopes’ up to −5.00 D. In this example, the lenses58 a and 58 b are each packaged in a suitable sachet (not separatelyillustrated).

In FIG. 15, part 52 comprises a compartmented container 56 aaccommodating 20 different lenses 58 a covering −5 D in −0.25 Dincrements of central corrective power while part 54 comprises acompartmented container 56 b also with 20 lenses 58 b covering −5 D ofnegative central power in −0.25 D increments. The respective incrementof central power is written above lenses 58 a of part 52 as indicated bybracket 59 a and the central powers of lenses 58 b of part 54 aresimilarly indicated at 59 b. The peripheral defocus of lenses 58 a arecollectively indicated by bracket 57 a and the peripheral defocus oflenses 58 b are collectively indicated by brackets 57 b. Containers 56 aand 58 a can be differently color-coded, for example container 56 a maybe yellow and 58 a may be red, and all the lens sachets of eachcontainer are similarly differentiated using the same color codes—aswell as bearing both the central power and the peripheral defocus of theenclosed lens(es), to minimize the chance of a lens sachet being placein the wrong part of kit 50 or the chance of the wrong sachet/lens beingselected for trial or use. For convenience of use, lenses 58 a and 58 bare arrayed in their respective containers 56 a and 56 b according totheir increments of central power, though this need not be done in thelinear fashion shown in FIG. 15. The lenses 58 a of part 52, in thisexample, together include four steps of peripheral power and, thus, formfour sub-sets of lenses, indicated by brackets 60 a, 61 a, 62 a and 64a. (The designs for these lenses are those of FIG. 14.) The peripheraldefocus of each sub-set is diagrammatically indicated by the height ofthe shaded portion of each lens and by the power number having a plussign associated with the respective brackets. Thus sub-set 60 a hasthree lenses 58 a each having a peripheral defocus of 1.0 D, sub-set 61a has 8 lenses each with a peripheral defocus of 1.5 D, sub-set 62 a has4 lenses each with a peripheral defocus of 2.0 D and sub-set 64 a hasfive lenses 58 a each with a peripheral power of 2.5 D. Similarly, part54 has four sub-sets 60 b, 61 b, 62 b, and 64 b having three, eight,four and five lenses 58 b with peripheral defocus steps marked +1.5 D,+2.0 D, +2.5 D and +3.0 D respectively.

Lens kit or set 50 can be used in the following manner. The practitionermakes a normal estimate or measurement of central refractive error ofthe patient's eyes using existing equipment and techniques employed forthe prescription of conventional corrective lenses, and reviews thepatient history to judge whether the patient is likely to suffer fromprogressive myopia. If not, a lens from part 52 of kit 50 with theappropriate corrective central power is selected and tried; if so, alens from part 54 is selected and tried. If the patient is not satisfiedwith the acuity of central vision provided by the selected lens, thelens with the next adjacent central power from the same part of the kitis tried. If a patient who is trial-fitted with a lens from part 54finds the peripheral blur excessive, the lens with the same centralpower in part 52 of the kit can be substituted. In either case, theclinician can be highly confident that the selected lens will act toinhibit the progression of myopia in the patient to some degree bybringing the peripheral focus onto or in front of the peripheral retinato provide the desired stimulus for inhibiting further eye growth. Wherekit 50 is one of contact lenses, it can be used to dispense finishedlenses to the patient or to make the appropriate order for supply from awholesaler or manufacturer. Where kit 50 is one of finished trialspectacle lenses and the clinic has its own lens finishing grindingand/or polishing facility, it may supply finished lenses to the patient;otherwise, orders for such lenses are placed with manufacturers in theconventional manner.

Two further types of sets, kits or stocks formed in accordance with theprinciples of this invention are illustrated in FIGS. 16 and 17.Furthermore FIG. 16 illustrates two different contact lens kits, sets orstocks 70 a and 70 b, each comprising a box, tray or drawer 72 having aplurality of compartments 74, each of which stores multiple sachets 76of contact lenses (not separately shown) having the same centralcorrective power. For convenience, only four sachets 76 are shown ineach compartment 74. The central power of the lenses in each compartment74 is written above or below each compartment on labels 78. It will beseen that the central power of the lenses ranges from −0.25 D to −6.0 Din 0.25 D increments.

In kit, set or stock 70 a, the sachets 76 in each compartment 74 notonly have the same central power but have the same peripheral power;that is, the lenses in each compartment are identical so that they canserve as a combination trial kit and supply stock. Each sachet isclearly identified with the central corrective power and, while theperipheral power need not be included in this example, it is preferablethat all the sachets of the kit are coded (for example by color) to showthat they belong to one consistent series or kit type. The peripheralpowers of the lenses in the compartments conform to the median power ofthe surveyed population for the respective central corrective powersaccording to the third column of FIG. 12. That is, no two lenses of thestock or kit 70 a with different central powers have the same peripheralpower; conversely, each central power is associated with a uniqueperipheral power. The lenses of kit or stock 70 a therefore have theminimum positive therapeutic effect.

In kit, set or stock 70 b, lenses with multiple therapeutic levels butthe same central power are housed in each compartment 74, the label 78of the compartment identifying the respective central power of thelenses therein. Each sachet 76 of each compartment is coded to indicatethe level of therapeutic effect and preferably has writtenidentification of central power, peripheral power and treatment level.In this example, sachets 76 with four different levels of treatment arecontained in each compartment 74, the lowest being that of kit 70 adescribed above and taken from the third column of FIG. 12, secondlowest being taken from the second last column of FIG. 12, the secondhighest being taken from the second last column of FIG. 13 and thehighest being taken from the last column of FIG. 13. This kit, set orstock of lenses is then used in essentially the same manner as kit orset 50 described with reference to FIG. 15, except that the clinician isnow given a wider discretion to prescribe according to his or herassessment of the patient's propensity to progressive myopia from thepatient history—which, of course, will include familial history ofmyopia.

The final example of the trial set or kit is a seven-lens trial set orkit 80 of add-on lenses 82 for spectacles diagrammatically illustratedby FIG. 17, set or kit 80 comprising a rack 84 with sections or troughs86, which hold add-on lenses having plano central power and differentsteps/levels of peripheral power or defocus. In this case, sections 86have labels 88 to indicate the step/level of added peripheral power ordefocus, which is from +1.0 D to +2.5 D in 0.25 D increments andcorresponds to the ‘Mild Add’ option of the table of FIG. 12 (except forthe finer 0.25 steps) of peripheral defocus. Since the add-on lenses 82of kit 80 may not all have a common base curve, or other kits like thiswith sets of lenses having different base curves may be used, it will beconvenient for the base curve of each add-on lens to be identifiedadditionally by labels 90. However, as in previous examples, it is alsodesirable to mark the lenses or their sachets (if provided) to identifythe peripheral power and the base curve.

The manner of use of kit or set 80 is similar to that described for kitor set 50 (FIG. 15). The practitioner checks central refractive error ofthe patient's eyes, judges the patient's propensity for progressivemyopia from patient history, selects an add-on lens with a level orperipheral defocus appropriate to the judged propensity and tries theselected add-on lens on the patient's habitual spectacle lens or on asemi-finished trial base lens with the appropriate central power. If thepatient finds the peripheral blur excessive, an add-on lens with thenext lower level of peripheral defocus is tried until patient acceptanceis obtained. A final spectacle lens may then be ordered or finishedusing an in-house grinding and polishing facility. The ability toprovide so many levels of peripheral defocus from a small set or kit oflenses is an obvious advantage.

Turning more specifically to the anti-myopia ophthalmic devicesthemselves, and more specifically to ophthalmic lenses such as contactlenses, as noted above the peripheral power may be presented in aperipheral power profile wherein the peripheral power changes withradial distance, such that the peripheral power profile exhibits theperipheral power values located at a determined distance from thecentral axis. Previously the peripheral power profile of ophthalmiclenses was left the same or adjusted to reduce spectacle distortion orimprove central vision. Due to the lower visual acuity of the peripheralretina, correcting the peripheral refraction was not seen as significantimprovement.

As mentioned above, the peripheral defocus of the lens is determined bythe differential between the central power for the ophthalmic lens andthe peripheral power at a particular point on the peripheral powerprofile. An ophthalmic device, according to the present invention, iscontemplated to have a differential lens power (peripheral defocus ofthe lens) that is a function of the central sphere power. However,considerable individual variability in differential refraction(peripheral minus central) has been observed among both children andadults of comparable central refractive status. As a consequence, theuse of an anti-myopia ophthalmic/contact lens with an average, single,peripheral defocus/differential lens power may overcorrect theperipheral retina in some myopes, but undercorrect the peripheral retinain other myopes, depending on the individual peripheral defocus of aparticular eye. The optical effect for under-correction may be aresidual amount of hyperopic defocus in the peripheral retina, whichwould also create a stimulus for axial eye growth and worsening myopia.On the other hand, the optical effect for severe overcorrection of theperipheral retina may be an excessive amount of myopic, peripheraldefocus, which not only could hamper peripheral vision but also causeperipheral form vision deprivation resulting in further axial eye growthand myopia progression. Using an anti-myopia contact lens with anabove-average, single, peripheral defocus/differential lens power suchthat in most progressing myopes peripheral hyperopia is converted toperipheral myopia would prevent under-correction in some myopes, butcreate severe over-correction in other myopes with the above-mentionedconsequences.

In a series of lenses according to the present invention, each lens hasa differential lens power (amount of peripheral defocus) targeted at theaverage relative peripheral refraction for a given central sphere power.A lens with a greater than average peripheral defocus can be produced.Alternatively, a lens with a lesser than average peripheral defocus canbe produced. This means that while that peripheral defocus for the lenscan be greater or lower than the determined average, the amount ofperipheral defocus varies as a function of the particular central spherepower so as to produce lenses that adequately correct a variation in thelevel of peripheral refraction. In an alternative embodiment, ophthalmiclenses may be customized based on a particular individual's determinedlevel of peripheral refraction. As such, after determining theparticular individual's needed amount of peripheral defocus/differentiallens power, customized ophthalmic lenses are manufactured.

The relationship between central power and peripheral defocus of thelens can be, at a minimum, a first order (linear) relationship such thatthe peripheral defocus increases as a constant function of the centralsphere power for each lens. While a linear relationship fits thediscovered refractive relationship between the central and peripheralrefractions, this could be extended to higher order or non-polynomialrelationships to produce a more refined non-linear relationship. Theresult is an increasing peripheral defocus from a minimum at low myopia(−0.25 D) to a maximum at high myopia (−30.00 D) or as limited byoptical design constraints. This is unlike other optical correctionssuch as presbyopia where the loss of accommodation is not related toamount of myopia. For the correction of presbyopia there is no increasein additional power as a function of the refractive myopia.

This relationship provides a more precise induced peripheral refractivechange than using a fixed peripheral defocus for the lens. Thisrelationship is based on the experimental finding that an eye's centralto peripheral refraction may increase with the amount of myopia. Whenapplied to a power range of inventoried anti-myopia lenses theexperimentally determined mean central to peripheral refraction would beused as the function to design the lens's optical peripheral defocus foreach lens sphere power.

In additional study results on the peripheral refraction of the eyewhich were obtained in the CIBA Vision Research Clinic, it was shownthat the most hyperopic refractive foci (the sphere meridian) of amyopic eye can vary from less than between approximately 0.25 D and 4.00D (at −6.00 D, and even greater for higher minus power is expected)difference from central axis to 30 degrees off-axis. More desirably, at30 degrees off axis, the range can be approximately between 0.25 D and3.0 D, and even more desirably between approximately 0.25 D and 2.5 D.Between central axis and 40 degrees off-axis, that difference increasesand can be approximately between 0.50 D and 6.00 D. Evaluation ofoptical designs of soft contact lenses where the peripheral defocus wasmore positive has shown that high (2.50 D) differential refractions canbe corrected (see FIG. 20). However, the same peripheral defocus designworn on an eye with 0.75 D differential refraction overcorrects theperipheral refraction and produces obvious peripheral blur for thewearer.

FIG. 18 represents the central and peripheral auto refraction of an eyewhich is emmetropic. There is very little relative peripheral hyperopia(less than 0.50 D at 30 degrees) and in this particular case therelative peripheral hyperopia is −0.62 (at 30 degrees off axis) minus−0.62 D (at central axis), which is 0.00 D.

FIG. 19 represents the peripheral auto refraction of an eye which ishighly myopic; in this case wearing a conventional soft contact lens formeasurement purposes with an auto refractor. There is much more relativeperipheral hyperopia (greater than 2.00 D at 30 degrees off axis) and inthis particular case the relative peripheral hyperopia is 2.75 D (at 30degrees off axis) minus 0.37 D (at ten degrees off axis), which is 2.37D.

FIG. 20 represents a myopic eye with a subjective central refraction ofabout −1.50 D. The relative peripheral hyperopia in this particular caseis low at −0.25 D (at 30 degrees off axis) minus −1.00 D (at ten degreesoff axis), which is 0.75 D. The additional refractive data was takenthrough a soft contact lens designed to correct high levels of relativeperipheral hyperopia. The effect of this lens correcting the eye is nowrelative peripheral myopia and in this particular case the relativeperipheral myopia is −3.25 D (at 30 degrees off axis) minus −2.50 D (atten degrees off axis), which is −0.75 D. Along with the overall myopicshift of the auto refraction, this change in peripheral auto refractionwas too much and caused subjective distortion of peripheral vision.

FIG. 21 represents the peripheral auto refraction of the same highlymyopic eye as in FIG. 19, in this case −6.00 D imaged through a −4.00 Dcorrection lens for measurement purposes with an auto refractor. Theadditional refractive data was taken through the soft contact lensdesigned to correct high levels of relative peripheral hyperopia as usedin FIG. 20. The effect of this lens correcting the eye is much lessrelative peripheral hyperopia, and in this particular case the relativeperipheral hyperopia is −4.25 D (at 30 degrees off axis) minus −4.62 D(at ten degrees off axis), which is 0.37 D. Along with the lesseroverall myopic shift of the auto refraction, this change in peripheralauto refraction was less and caused no subjective distortion ofperipheral vision.

FIG. 22 represents the results of a study of Schmid in which the spherepower in minus cylinder notation was measured centrally and at 20degrees in the nasal, temporal, inferior and superior retina with a ShinNippon K5001 open-field auto-refractometer in both eyes of six youngadult volunteers during cycloplegia. Plotting the relative peripheralrefraction for sphere power (peripheral minus central sphere power) foreach location vs. central sphere power revealed an inverse correlation.Statistical significance was reached for the mean of all four peripherallocations combined.

FIG. 23 represents more details from the Schmid study. All fourquadrants showed the same trend of increasing relative peripheralhyperopia with increasing central myopia. Individually, statisticalsignificance was reached for the inferior and superior quadrants wherethe change is slightly larger.

Correlation analysis between subjective vision quality and objectiveauto-refraction in the retinal periphery of patients who reporteddifferences in vision quality between lenses of various peripheraldefocus powers revealed that over-correction limits exist, beyond whichvision quality is not acceptable. Turning to FIG. 24, there is shown arepresentation of the effect of peripheral refraction on the rating ofside vision quality for the lenses, using a scale from 0-10. Symbolsindicate those patients subjects who answered “no” (circles) or “yes”(triangles) to the question whether vision quality is sufficient to wearthe lens all the time.

The plot as shown in FIG. 24 is in terms of sphere refraction (“Sph”;left side of plot) and sphere equivalent refraction (“M”; right side ofplot) as measured at 30 degrees in the temporal retina (nasal field)(“T30”) by auto-refractometry. If, for example at 30 degrees in thetemporal retina (nasal field), the lens produces a sphere refractionbelow about +0.25 D (i.e. on the retina or in front of the retina), thenvision quality is unacceptable as indicated by all patients answering“no” to the question whether vision quality is sufficient to wear thelens all the time. This is shown in the plot in the shaded left side ofthe “T30 Sph” portion. Similarly, for a sphere equivalent refractionbelow about −2.50 D (i.e. further in front of the retina than −2.50 D),vision quality is unacceptable as indicated by all patients answering“no” to the question whether vision quality is sufficient to wear thelens all the time (shaded left side of the “T30M” portion.). Therefore,it can be seen that over-correction of peripheral refraction leads toreduced subjective vision. In particular the sphere meridian should notbe corrected to less than +0.25 D and the sphere equivalent meridian toless than −2.50 D. The correlation analysis also indicated that lensrejection is chiefly caused by decreased peripheral vision as opposed tocentral vision. The identification and application of theseover-correction limits substantially facilitates the lens fittingprocedure, and helps reduce vision degradation and lens rejection by thepatient when correcting peripheral defocus and controlling refractiveerror development.

Turning now to FIG. 25, there is shown a scatterplot of both spheremeridian and sphere equivalent (SEQ) data which plots the central sphereequivalent refraction (in diopters) against the refractive difference(also in diopters) between central and 30 degree nasally offsetautorefractions. These data were obtained from a largely adultpopulation made up of Caucasian subjects. As can be seen in FIG. 25, forcentral sphere equivalent (SEQ) refractive errors between +0.50 and−5.00 D, there is a significant increase the peripheral refractivedifferential with increase in myopia. The rate of increase or slope of abest fit line for these data is 0.14 D/D for sphere meridian and 0.18D/D for the SEQ. The intercepts (x=0 or plano refractive error) are+0.53 D for sphere meridian and 0.05 D for the SEQ. Therefore, targetingcorrection or reduction of peripheral refractive differentials foreither the sphere meridian or SEQ requires an increase at about the samerate with central SEQ refractions.

In FIG. 26, there is shown a scatterplot of the central sphereequivalent (SEQ) refraction data that was shown in FIG. 25, which isalso plotted with data of the central sphere equivalent (SEQ)refractions obtained from a population made up of Asian (Chinese) childand adolescent subjects. These data are plotted against the sphereequivalent refractive difference (also in diopters) between central and30 degree nasally offset autorefractions. Comparison of Caucasian andAsian populations, with SEQ refractive errors between −0.50 and −4.00 D,shows a significant difference in the increase the peripheral refractivedifferential with increase in myopia. The rate of increase or slope of abest fit line for these data is −0.19 D/D for the Caucasian populationmeasured and −0.35 D/D for the Asian population measured. Therefore,targeting correction or reduction of peripheral refractive differentialrequires an increase with central SEQ refractions (as noted above withrespect to FIG. 25); however, that increase may change depending on thetarget population's makeup or environmental demographics.

In certain embodiments, varying the peripheral defocus for each spherepower still may not cover the full range of relative peripheralrefractions needed to fit all myopic patients' relative peripheralhyperopic defocus without clinically significant over and undercorrection in some individuals. In this case, the target correction ofthe ophthalmic lens can be matched to the change in peripheralrefractive differential and an additional variation such as providing anaverage, a lower than average and a higher than average central toperipheral differential lens power (peripheral defocus) may be neededfor each sphere power. While varying the peripheral defocus with centralsphere power allows for the change in the average relative peripheralhyperopic defocus, the wide range in the population may need a higherand lower optical design factor to further avoid clinically significantover or under correction of individual patients' relative peripheralrefraction. In the example shown in FIG. 27, the target correction or“Average SEQ” correction is to correct the peripheral refractive SEQdifferential to +0.75 diopters, and to account for a wide range in thepopulation further higher and lower peripheral refractive SEQdifferential targets are shown by the dashed lines designated “High SEQ”and “Low SEQ”. In this combination the average central to peripheraldifferential power will still increase with the minus sphere power tocorrect for the overall increase in central to peripheral differentialrefraction with increasing myopia.

In an alternative embodiment, a contact lens may be designed with anegative power differential to provide hyperopic defocus in the centraland retinal periphery for the stimulation of axial eye growth inhyperopic eyes. In a further alternative embodiment, a contact lens isdesigned with a sphero-cylindrical central power for correctingastigmatism. In this case, either the sphere part or the sphericalequivalent (sphere +half of the cylinder) of the central power is usedas central sphere power for defining the desired peripheral defocus ofthe lens. A further alternative embodiment of the present inventionwould include custom prescription of the peripheral defocus based on thepatient's individual central to peripheral refraction of the eye. Thiswould be a custom ‘made to order’ correction and not the more commoninventoried approaches as are described above.

It will be appreciated that many modifications of or additions to thesets, kits or stocks of lenses, and to lenses or lens components per se,described in the example, or to their methods of use, can be made bythose skilled in the art without departing from the scope of theinvention as set out in the following claims.

The invention claimed is:
 1. A set, kit or stock of pre-manufacturedlenses for use in the provision of an anti-myopia lens for an eye of amyopic patient, wherein: each lens of the set, kit or stock has acentral optical axis and a central optical zone surrounding andincluding said axis, said central optical zone has a negative correctiverefractive power between plano and −6.0 D, for correcting a positivecentral refractive error of a myopic eye, said negative correctiverefractive power varying in increments of a central refractive powerwithin said set of lenses, each lens has a peripheral optical zonesurrounding said central zone, said peripheral zone includes an incidentangle with respect to the optical axis of about 30 degrees, saidperipheral zone of each lens has a positive peripheral refractive powerrelative to the refractive power of the central zone of that lens tothereby provide myopic peripheral defocus, said peripheral refractivepower increases with increase of central refractive power within the setof lenses, said peripheral defocus of any lens within the set, kit orstock of lenses is not greater than about 3.5 D, and the lenses of theset, kit or stock are arranged in an orderly manner according to centralrefractive power, peripheral refractive power and/or peripheral defocus;whereby a clinician is enabled, by selecting a lens for corrective powerto provide or procure a lens to inhibit progression of myopia in thepatient's eye without needing to first measure peripheral refractiveerror in the eye and to order a lens with customized peripheral power.2. A set, kit or stock of pre-manufactured lenses according to claim 1,wherein: the increment of central refractive power is about −0.25 D, thecentral refractive powers of the lenses fall within the range of about−0.25 D to about −6.0 D, and the peripheral defocus of the lenses variessubstantially proportionally with variation of the central refractivepowers of the lenses within the range of +0.5 D to +3.0 D.
 3. A set, kitor stock of pre-manufactured lenses according to claim 2, wherein: theperipheral defocus of the lenses of the set, kit or stock of lensesincreases in steps with increasing central power such that multiplelenses with adjacent increments of central power have the sameperipheral defocus, whereby understanding or use of the set, kit orstock of lenses is facilitated by the clinician, manufacturer and/or thepatient.
 4. A set, kit or stock of pre-manufactured lenses according toclaim 1, wherein: there are multiple subsets of lenses such that eachsubset comprises a plurality of lenses having the same centralrefractive power but different levels of peripheral defocus; whereby, aclinician who knows the positive central refractive error of the myopiceye is enabled to conveniently (i) select the subset of lenses havingthe central refractive power judged to best correct said measuredcentral error, (ii) select the lens from within the selected subsetjudged to have the level of peripheral power most appropriate to thepatient's propensity for progressive myopia having regard to patienthistory, and (iii) try the selected lens on the eye to assess thepatient's tolerance to peripheral blur caused by the selected lens.
 5. Aset, kit or stock of pre-manufactured lenses according to claim 4,wherein: there are three levels of peripheral power in each said subsetof lenses comprising low, medium and high levels of peripheral defocus;whereby the clinician who has found that a selected lens having mediumor high level of peripheral defocus is not acceptable to a patient isenabled to then select a lens with the same central power but a lowerlevel of peripheral defocus.
 6. A set, kit or stock of pre-manufacturedlenses according to claim 1, wherein: the lenses of the set, kit orstock are contact lenses for trial or dispensing, there are about 24increments of central refractive power, said central refractive power ofthe lenses in the set, kit or stock ranges from −0.25 D to about −6.0 D,each increment of central power is about −0.25 D, each lens of the set,kit or stock of lenses has a unique peripheral defocus, and the amountof peripheral defocus of the lenses in the set, kit or stock of lensesincreases substantially proportionally with increasing centralrefractive power of the lenses in the set, kit or stock of lenses.
 7. Aset, kit or stock of pre-manufactured lenses according to claim 1,wherein: the lenses of the set, kit or stock are contact lenses fortrial or dispensing, there are about 24 increments of central refractivepower, said central refractive power of the lenses in the set, kit orstock ranges from −0.25 D to about −6.0 D, each increment of centralpower is about −0.25 D, there are at least three steps of peripheralrefractive power or defocus, and each of said steps is about +0.5 D. 8.A set, kit or stock of pre-manufactured lenses according to claim 1,wherein the patient uses a habitual lens that has a negative refractivepower for correcting central refractive error in the myopic eye: thelenses of set, kit or stock are trial spectacle lenses for use togetherwith the patient's habitual lens, each lens of the set, kit or stock hasplano central refractive power and a different peripheral power fromother lenses of the set, kit or stock, each lens of the set, kit orstock is adapted for location in juxtaposed axial alignment with thehabitual lens when fitted to the eye, and the lenses of the set, kit orstock are arranged in an orderly manner according to peripheral power,whereby a clinician is enabled to conveniently (i) select a lens fromthe set, kit or stock judged to have the level of peripheral power mostappropriate to the patient's propensity for progressive myopia havingregard to patient history, and (ii) try the selected lens in conjunctionwith the habitual lens on the eye to assess the patient's tolerance toperipheral blur.
 9. A set, kit or stock of pre-manufactured lensesaccording to claim 8, wherein: the peripheral defocus of the lensesranges between about +0.5 D and about +2.0 D, and the peripheral powerof the lenses of the set, kit or stock of lenses varies in incrementsnot greater than about +0.5 D.
 10. A set, kit or stock ofpre-manufactured lenses according to claim 1 wherein the lenses aresubstantially rotationally symmetric in that the peripheral defocus issubstantially the same for each peripheral quadrant of the lens.
 11. Aset, kit or stock of pre-manufactured lenses according to claim 1wherein: the peripheral defocus of the lenses of the set, kit or stockof lenses applies to the nasal quadrant or to the temporal quadrant ofthe lens so that, when a lens of the set, kit or stock of lenses is inuse by a patient, the measured peripheral defocus of the lens affectsthe temporal or the nasal quadrant of the patient's retina,respectively.